Protein kinase D1 upregulates expression and activity of extracellular signal-regulated kinase 1/2 and EGFR in human hTert keratinocytes

Immortalized hTert keratinocytes have been obtained from normal human epidermal keratinocytes, which were infected with amphotropic retroviral vectors encoding hTert, the catalytic subunit of telomerase, followed by spontaneous loss of p16^INK4a function. There are no any data in the literature concerning transduction pathways participating in regulation of proliferation and/or differentiation of this cell line, probably because it was previously supposed that immortalization of the cells does not disrupt other normal growth control mechanisms. In this study, we explored the effects of PKD1 inhibition in hTert keratinocytes, using siRNA approach, on expression and activation of ERK1/2 and EGFR which acts to promote proliferation and survival in normal human epidermal keratinocytes. Treatment of cultured hTert keratinocytes with siRNA for PKD1 effectively diminished protein levels of the kinase, ERK1/2 expression and activity, EGFR expression and activity and according to our previous results in K10 and involucrin expression. It is possible that PKD1, ERK1/2 and EGFR have adverse effects in immortalized human hTert keratinocytes compared to normal human epidermal keratinocytes in regulation of proliferation and differentiation. We showed for the first time that ERK1/2 MAPK, which are considered to be constitutively expressed kinases in mammalian cells, are inducible enzymes regulated by PKD1 in hTert keratinocytes.